Thick plate type joint lock for ladder connection

ABSTRACT

A think plate type joint lock for ladder connection comprises an inner plate and an outer plate connected in a relatively rotating way, and a positioning shaft sleeve for locking the inner plate and the outer plate. In addition, a rotation limiting column is arranged on the outer plate, and a groove for resisting the limiting column is arranged on the inner plate. The limiting column and the groove restrict rotation of the inner plate relative to the outer plate, thus improving a load bearing capability and security of a ladder.

FIELD OF THE INVENTION

The present invention relates to a structure member for ladder jointing, in particular to a thick-plate hinge for ladder jointing.

BACKGROUND OF THE INVENTION

In 1970s, an American Hal Wing designed and manufactured a telescopic multi-purpose ladder, which was commonly known as “Little Giant”. Through years of development, Little Giant ladders have taken the lead in the industry and are popular around the world.

A key technique of Little Giant ladders is the jointing part, called thick plate hinge that joints the upper ladder section and a lower ladder section. Please see FIG. 1-4. The thick-plate hinge 10 comprises an inner plate 11 and outer plates 12 that are folded on outer sides of the inner plate, the inner plate 11 and outer plate 12 are relatively rotatable; the thick-plate hinge 10 further comprises a positioning shaft sleeve 13 designed to lock up and position the inner plate 11 and outer plates 12, wherein, the positioning shaft sleeve 13 has a shaft 14 and a lock pin 15, the outer plate 12 has a stop stub 16 fixed on it, and the stop stub 16 butts against an outer arc surface 110 of the inner plate 11 when the relative rotation angle between the inner plate 11 and the outer plate 12 reaches 180°. The stop stub 16 can improves the bearing performance of the thick-plate hinge 10.

Via the positioning shaft sleeve 13, the inner plate 11 and outer plates 12 of the thick-plate hinge 10 can be locked up when they rotate to a preset angle in relation to each other, for example, the inner plate 11 and outer plates 12 can be locked up via the positioning shaft sleeve 13 when the unfolding angle is 0°, 36°, or 180°. With the structure described above, two thick-plate hinge 10 can be connected between an upper ladder section and a lower ladder section, so that the ladder can be transformed into a double-sided ladder (with 36° unfolding angle) or a long straight ladder (with 180° unfolding angle), to attain multiple purposes.

When the ladder is transformed into a straight ladder, both the inner plate and the outer plate of the two thick-plate hinges are unfolded to 180°. When tested in unexpected state or under specific conditions, e.g., tested as per the ladder standards of USA or that of Australia, the tested ladder must be able to bear the test load in a case that either thick-plate hinge work in fail state (the lock pin 15 is drawn out of the lock pin hole). In the prior art, in case either thick-plate hinge in fail state, though the thick-plate hinge still has some bearing capability obtained from the butting of the stop stub 16 and outer plate 12, the stop stub would have displacement on the outer arc surface, since the bearing surface of the inner plate that butts against the stop stub is arc surface; consequently, the bearing angle between the upper ladder section and the lower ladder section is greater than 180°; in addition, the higher the load is, the greater the displacement would be, and it lead to larger relative rotation angle between the inner plate and the outer plate. As a result, the overall bearing capacity of the ladder would be degrade, and the entire ladder is more possible to fail in the test. In that case, the solution in the prior art is to increase the strength of the thick-plate hinge or the strength of the entire ladder to improve the bearing capacity of the entire ladder, which would inevitably increase the cost of the entire ladder severely.

SUMMARY OF THE INVENTION

To overcome the drawbacks in the prior art, the present invention provides a new thick-plate hinge, which has better bearing performance and is safer and more reliable.

To attain the object described above, the present invention provides a thick-plate hinge for ladder jointing, comprising an inner plate and outer plates that are folded on both outer sides of the inner plate, the inner plate and outer plates are relatively rotatable; the thick-plate hinge further comprises a positioning shaft sleeve that is designed to lock up and position the inner plate and outer plates, and the outer plate has a stop stub fixed on it, wherein, the inner plate has a slot designed to limit the displacement of the stop stub, and the stop stub will enter into the slot partially or entirely when the relative rotation angle between the inner plate and the outer plate reaches 180°.

Preferably, the stop stub is a cylindrical stub, the bottom surface of the slot is an inwardly concaved arc surface, and the arc surface is tangentially fit the outer circumferential surface of the stop stub. More preferably, the radius of the arc surface is greater than or equal to the radius of the stop stub.

Preferably, the depth of the slot is greater than or equal to the radius of the stop stub.

With the technical solution described above, in the thick-plate hinge provided in the present invention, by providing the slot on the inner plate, the slot can limit the displacement of the stop stub when the relative rotation angle between the inner plate and the outer plate reaches to 180°; thus, the thick-plate hinge has better bearing performance, and is safer and more reliable

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of a thick-plate hinge for ladder jointing in the prior art, with the thick-plate hinge unfolded to 36°;

FIG. 2 is a rear view of the thick-plate hinge for ladder jointing in the prior art, with the thick-plate hinge unfolded to 36°;

FIG. 3 is a left view of the thick-plate hinge for ladder jointing in the prior art, with the thick-plate hinge unfolded to 36°;

FIG. 4 is a front view of the thick-plate hinge for ladder jointing in the prior art, with the thick-plate hinge unfolded to 180°;

FIG. 5 is a front view of the thick-plate hinge for ladder jointing provided in the present invention, with the thick-plate hinge unfolded to 36°;

FIG. 6 is an enlarged view of portion A of the thick-plate hinge shown in FIG. 5;

FIG. 7 is a rear view of the thick-plate hinge for ladder jointing provided in the present invention, with the thick-plate hinge unfolded to 36°;

FIG. 8 is a front view of the thick-plat hinge for ladder jointing provided in the present invention, with the thick-plate hinge unfolded to 180°;

FIG. 9 is a schematic diagram of a ladder mounted with the thick-plate hinge for ladder jointing provided in the present invention in performance test, with the thick-plate hinge unfolded to 180°.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Thereinafter, a preferred embodiment of the present invention will be described in detail, with reference to the accompanying drawings.

Please see FIG. 5-8. The present invention provides a thick-plate hinge 20 for ladder jointing, comprising an inner plate 21 and outer plates 22 that are folded on both outer sides of the inner plate, the inner plate 21 and outer plate 22 are relatively rotatable; the thick-plate joint lock 20 further comprises a positioning shaft sleeve 23 designed to lock up and position the inner plate 21 and outer plates 22, the positioning shaft sleeve 23 is provided with a shaft 24 and a lock pin 25, the outer plate 22 has a stop stub 26 fixed on it, and the inner plate 21 has a slot 27 that limits the displacement of the stop stub 26.

Please see FIG. 8. The stop stub 26 will enter into the slot 27 entirely when the relative rotation angle between the inner plate 21 and the outer plate 22 reaches 180°.

In this embodiment, the stop stub 26 is a cylindrical stub, the bottom surface of the slot 27 is an inwardly concaved arc surface, the outer circumferential surface of the stop stub 26 is tangentially fit the arc surface of the slot, and the radius R of the arc surface of the slot 27 is greater than the radius of the stop stub 26. The depth H of the slot 27 is greater than the radius of the stop stub 26.

Please see FIG. 9. Two thick-plate hinges 20 can be connected between an upper ladder section 31 and a lower ladder section 32, so that the ladder can be transformed into a double-sided ladder (with 36° unfolding angle) or a long straight ladder (with 180° unfolding angle), to attain multiple purposes. When a ladder 30 mounted with the thick-plate hinges 20 provided in the present invention is unfolded to 180° and tested in ‘single joint lock test’, the ladder is obliquely supported on a vertical wall 40 at a certain angle, and then one thick-plate hinge 20 is manipulated to fail state (the lock pin 25 is drawn out of the lock hole); in that case, the function of the failed hinge is still able to assist the another thick-plate hinge effectively to bear the heavy load 50 hung on the upper section 31 of the tested ladder, since the stop stub 26 of the failed hinge enters into the slot 27.

Compared to the prior art, the ladder 30 that employs the thick-plate hinge 20 provided in the present invention will not be unfolded to an angle greater than 180°; therefore, the ladder has greatly improved bearing performance, and is safer and more reliable.

The above embodiments are provided only to elaborate the technical idea and features of the present invention so that those skilled in the art can understand the present invention and implement accordingly, instead of constituting any limitation to the scope of protection of the present invention. Any equivalent modification or embellishment made on the basis of the substantial spirit of the present spirit shall be deemed as falling into the scope of protection of the present invention. 

1-5. (canceled)
 6. A thick-plate hinge for a ladder joint, comprising: an inner plate having a slot, an outer plate having a stop stub and rotatably connected to the inner plate, wherein the stop stub is configured to limit the rotation of the inner plate and the slot is configured to engage the stop stub, and a positioning shaft sleeve in communication with the inner plate and the outer plate, wherein the position shaft sleeve has a locking pin and configured to lock the inner plate and the outer plate at a predetermined position.
 7. The thick-plate hinge for a ladder joint according to claim 6 wherein the stop stub enters into the slot when the inner plate and the outer plate are in an unfolded position.
 8. The thick-plate hinge for a ladder joint according to claim 6 wherein the stop stub is a column stub and the slot is an inwardly slot.
 9. The thick-plate hinge for a ladder joint according to claim 8 wherein the stop stub is a cylindrical stub and the slot is an inwardly concaved arc slot.
 10. The thick-plate hinge for a ladder joint according to claim 9 wherein the radius of the slot is greater than or equal to the radius of the stop stub.
 11. The thick-plate hinge for a ladder joint according to claim 9 wherein the depth of the slot is greater than or equal to the radius of the stop stub.
 12. The thick-plate hinge for a ladder joint according to claim 1 wherein the stop stub will enter into the slot at least partially when relative rotation angle between the inner plate and the outer plate reaches 180°. 